Register for this year’s #ChromeDevSummit happening on Nov. 11-12 in San Francisco to learn about the latest features and tools coming to the Web. Request an invite on the Chrome Dev Summit 2019 website

Background video track optimizations (MSE only)

To improve battery life, Chrome now disables video tracks when the video is
played in the background (e.g., in a non-visible tab) if the video uses Media
Source Extensions (MSE).

You can inspect these changes by going to the chrome://media-internals page,
and filter for the "info" property. When the tab containing a playing video
becomes inactive, you'll see a message like Selected video track: []
indicating that the video track has been disabled. When the tab becomes active
again, video track is re-enabled automatically.

Figure 1.
Log panel in the chrome://media-internals page

For those who want to understand what is happening, here's a JavaScript code
snippet that shows you what Chrome is roughly doing behind the scenes.

Automatic video fullscreen when device is rotated

If you rotate a device to landscape while a video is playing in the viewport,
playback will automatically switch to fullscreen mode. Rotating the device to
portrait puts the video back to windowed mode.